PROJECT SUMMARY/ABSTRACT The significance of studying the distal aqueous drainage tract and its regulation is that the tract contributes significantly to aqueous outflow resistance. This outflow resistance is a major determinant of intraocular pressure (IOP). IOP is a key risk factor for glaucoma, the leading cause of irreversible blindness worldwide. We do not understand enough about how IOP is regulated. By what means IOP becomes dysregulated in glaucoma is mostly also unknown. The long-term objective of the project is to improve our understanding of IOP regulation, glaucoma pathogenesis and to develop more effective clinical therapy. Such improved therapy should better target the underlying mechanism of IOP elevation in a way that alters the natural course of glaucoma that would otherwise lead to blindness. The health benefits will be seen in better preservation of vision that positively impacts patients' lives. Background and scientific need. Surgically bypassing the trabecular meshwork is increasingly performed to lower IOP and treat glaucoma. IOP does not fall as far as might be expected once the high resistance meshwork tissue is bypassed, however. Significant resistance to outflow must then remain in the distal aqueous drainage tract situated between the trabecular meshwork and downstream blood vessels. It is thus important to understand the cellular organization of the distal aqueous drainage tract and its effect on outflow resistance, but we know very little about how it works. This represents an important gap in our scientific knowledge that is a barrier to better understanding and treating glaucoma. Innovation. We postulate that walls of the distal aqueous drainage tract have capacity to contract to alter the tract's caliber and dimensions. This provides a mechanism for regulating aqueous outflow resistance and IOP. We seek to identify molecular markers of contractility in the distal tract and determine their role in regulating aqueous humor outflow. We will study various mutant mice by 2-photon microscopy that resolves cells within tissues to address the specific aims to: (1) ascertain cellular characteristics of the distal aqueous drainage tract; (2) determine the extent to which contractile mechanisms are present and affect outflow by this pathway. Impact. The project seeks to improve our understanding of IOP regulation in health and disease and discover more effective ways to treat glaucoma.